As a conventional cutting insert, there is a cutting insert disclosed in the Patent Literature 1. The cutting insert described in the Patent Literature 1 has a substantially rhombus, plate-like shape, and includes a chip breaker groove on at least one of opposite end surfaces. The chip breaker groove is formed at a position including a vicinity of a corner portion of each end surface. The chip breaker groove includes a rake surface. A flank on which a cutting edge extends along the intersecting ridge line portion between the rake surface and the flank extends on a side surface connecting the two end surfaces with each other. The cutting insert includes a breaker protruding portion protruding toward a corner cutting edge in a circular arc shape at the corner portion. Further, the cutting insert is also disclosed that has a breaker protruding portion protruding toward a straight-line shaped cutting edge connecting to the corner cutting edge.